Preparation of uranium alum-inum alloys



This invention deals with a process of preparing uranium-aluminum alloys as they are used as fuel material in neutronic reactors, and in particular with the preparation of these alloys by the reduction of uranium chloride dissolved in a molten salt with aluminum metal.

Uranium-aluminum alloys have been prepared heretofore by simply melting the two metals. The so-called cryolite process has also been used for fliis purpose; this process comprises the reduction of uranium oxide with aluminum metal in a cryolite solution. Both of these processes require rather high temperatures because the melting point of eryolite and that of uranium is around 1000 C. Uranium chloride has also been reduced with aluminum metal in an equimolar aluminum chloride-alkali metal chloride solution; however, the uranium recovery there was not very complete. If the uranium is one of the fissiona-ble isotopes, U or U or enriched in either, quantiativeness of the process is of especially great importance.

The process of this invention represents an improvement over the last of the three processes described and does not have the drawbacks enumerated above.

It is an object of this invention to provide a process for the preparation of uranium-aluminum alloys from uranium chloride by which a yield of above 99% is obtained.

It is another object of this invention to provide a process for the preparation of uranium-aluminum alloys from uranium chloride for which only one reduction stage is required for a recovery of about 99%.

It is also an object of this invention to provide a process for the preparation of uranium-aluminum alloys from uranium chloride for which a comparatively low temperature can be used so that a greater selection of container materials is available.

It is finally also an object of this invention to provide a process of preparing uranium-aluminum alloys from neutron-irradiated fission-product-containing uranium oxide wherein reduction of the uranium compound and separation from fission products, such as alkali metals, alkaline earth metals, and rare earth metals, are accomplished simultaneously.

It has been previously found that an equimolar ratio of potassium chloride to aluminum chloride is necessary as the solvent for the uranium chloride to obtain good results in the reduction of uranium chloride with aluminum. When the salt mixture was precisely equimolar, a 9 7.4% reduction yield was obtained. However, with the slightest deviation from equimolarity, the yield was considerably reduced. This criticality of equitates IFatent are juxtaposed with the mole ratio used of aluminum chloridez-potassium chloride.

TABLE I 1 A1013 DU M K01 0.481- 1. OOiO. 09

0.685. 2. 58:l;0. 17 0.688. 3. Hill. 21

1.662.-- 0. 88i0. 0s 1.697--. 0. 83in. 41

It has been found by this invention that substitution of bromide for part of the chloride in the equirnolar double salt brings about a further improvement in the reduction yield and that the chloride anion to bromide anion ratio has a critical range. The substitution of bromide does not impair the dissolution of the uranium chloride in the double salt. It has been found that the critical range of chloridetbromide anions is that between 9 and 13, the preferred ratio being about 10. With this critical ratio the aluminum:alka1i metal ion ratio still has to be about equimolar and, more specifically, it ought to be within the range of 1.0:01. The criticality of the Cl-zBrratio with about equimolar Al:K ratios is illustrated in Table II. There a number of runs are summarized in which various quantities of potassium bromide were substituted for the potassium chloride of the equimolar double salt. Apart from the different Cl:Brmole ratio and a very slight variation in the A1:K ratio as indicated in Table II, the operating conditions were the same in all runs.

TABLE II ClzBr A1:K Mole Mole DU Ratio Ratio It is quite obvious from the above results that the reduction of uranium chloride with the aluminum and consequently the transfer of uranium into the metal phase was radically higher when the Cl-:Br ratio was within the range of from 9 to 13.

The process of this invention consequently comprises dissolving a uranium halide, in particular uranium chloride, in a roughly equimolar molten mixture of alkali metal and aluminum halides in which the halides are a mixture of chloride and bromide in a mole ratio (Cl 2B1 of 9 to 13; adding aluminum metal to the salt solution in a quantity several times that stoichiometrically required for the reduction of the uranium halide, whereby uranium metal is formed and alloyed with the excess of alumium; and separating the uranium-aluminum alloy from the salt.

Any uranium chloride, the trichloride, the tetrachloride, and the uranyl chloride, is suitable for the process of this invention. Instead of using uranium chlorides as the starting material, uranium oxides, U U0 or U 0 can be dissolved in the potassium-aluminum double salt. In this case uranium tetrachloride and/ or uranyl chloride are formed, which-as stated-are equally reducible by the process of this invention.

The bromide substitution can be made either in the alkali metal halide or in the aluminum halide; this means, either a mixture of alkali metal chloride, alkali metal bromide and aluminum chloride or a mixture of aluminum chloride, aluminum bromide and alkali metal chloride can be used for the process of this invention.

The temperature suitable for the process of this invention is between 700 and 750 C., 725 C. representing the optimal condition.

In order to maintain the salt composition as constant as possible when the starting material is uranium oxide, it is advisable, although not obligatory, to stir the aluminum halide-alkali metal halide-uranium oxide mixture with a chlorinating agent, such as carbon tetrachloride, chlorine gas and phosgene, so that the uranium oxide is converted to the chloride by the chlorinating agent and the aluminum halide-alkali metal halide ratio is not disturbed.

The aluminum is added after dissolution when a chlorinating agent is used. If the starting material is uranium chloride, the aluminum may be added after dissolution, or it may be incorporated simultaneously with the uranium halide.

In the following, an example is given to illustrate the process of this invention.

Example Two parallel runs were carried out in which uranium trioxide was dissolved in an about equimolar mixture of potassium halide and aluminum chloride. In run No. l the potassium halide was the chloride, while for run No. 2 a mixture of potassium chloride and potassium bromide was used. The operating temperature was 725 C.

After dissolution of the uranium oxide, which took about 15 minutes, aluminum metal was added, and the temperature of 725 C. was maintained for 40 minutes for equilibration; thereafter the tubes containing the reaction masses were quenched in water to halt the reaction. The salt and metal phases obtained were separated from each other mechanically and analyzed for their uranium contents.

The conditions of the two runs are shown more in detail in the table below together with the results.

Legend Run No. 1 Run No. 2

Wt. U03 (g.) 0.5866 0.6413 Wt. Salt Solvent (g.) 16.756 17.231 Al/K Mole Ratio in Salt 1.05:|=0.05 1.09:l=0.05 Ol/Br Mole Ratio in Salt 34.0 Wt. Aluminum (g.) 7.8395 7.3358 Wt. Alloy Phase (g.) 8.1230 7.7485 w/o Uranium in Alloy 4.31 6.44 g. Uranium in Alloy. 0.3502 0.4988 g. Uranium in Sa1t 0.1389 0.0364 Distribution Ooefi. of U (metalzsalt) 5.2 30.5 Fraction of Initial Uranium in Alloy (Percent). 71.7 93.5 Over-all Uranium Recovery, Percent 100.2 100.3

It is evident from the above data that a great improvement is obtained when part of the chloride is replaced by bromide.

It will be understood that this invention is not to be limited to the details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

1. A process of preparing uranium-aluminum alloys, comprising dissolving uranium chloride in a molten mixture of alkali metal halide and aluminum halide of a ratio between 0.9 and 1.1 in which the halides are a mixture consisting of chloride and bromide in a mole ratio, for chloride:bromide, of between 9 and 13; adding aluminum metal to the salt solution in a quantity several times that stoichiometrically required for the reduction of the uranium chloride, whereby uranium metal is formed and alloyed with the excess of aluminum; and separating the uranium-aluminum alloy from the salt.

2. The process of claim 1 wherein the mole ratio for the chloridezbromide is about 10.

3. The process of claim 1 wherein the salt mixture has a temperature of between 700 and 750 C.

4. The process of claim 1 wherein the alkali metal halide is a potassium halide.

5. The process of claim 1 wherein the salt is a mixture of alkali metal chloride, alkali metal bromide and aluminum chloride.

6. The process of claim 1 wherein the salt is a mixture of alkali metal bromide, aluminum chloride and alumium bromide.

7. A process of preparing uranium-aluminum alloys, comprising introducing uranium oxide into a molten mixture of potassium and aluminum halides in which the molar ratio of potassium halide and aluminum halide is between 0.9 and 1.1 and the halides consist of chloride and bromide in a mole ratio, for chloridezbromide, of between 9 and 13; passing a stream of carbon tetrachloride through the salt mixture while its temperature is maintained at between 700 and 750 0., whereby uranium chloride is formed; adding aluminum metal to the salt solution formed in a quantity several times that stoichiometrically required for the reduction of the uranium halide, whereby uranium metal is formed and alloyed with the excess of aluminum; and separating the uraniumaluminum alloy from the salt.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS OF PREPARING URANIUM-ALUMIUM ALLOYS, COMPRISING DISSOLVING URANIUM CHLORIDE IN A MOLTEN MIXTURE OF ALKALI METAL HALIDE AND ALUMINUM HALIDE OF A RATIO BETWEEN 0.9 AND 1.1 IN WHICH THE HALIDES ARE A MIXTURE CONSISTING OF CHLORIDE AND BROMIDE IN A MOLE RATIO, FOR CHLORIDE:BROMIDE, OF BETWEEN 9 AND 13; ADDING ALUMINUM METAL TO THE SALT SOLUTION IN A QUANTITY SEVERAL TIMES THAT STOICHIOMETRICALLY REQUIRED FOR THE REDUCTION OF THE URANIUM CHLORIDE, WHEREBY URANIUM METAL IS FORMED AND ALLOYED WITH THE EXCESS OFALUMINUM; AND SEPARATING THE URANIUM-ALUMINUM ALLOY FROM THE SALT. 